Nacional de Mexico 4-6-2 "Pacific" Type Locomotives

Class M-1 (Locobase 5343)

Described in the AERJ of February 1907, this trio were the most normal of the Pacifics delivered to the NdeM in the recent past. For its time, this was a rather big 4-6-2 with a boiler that, as the AERJ article noted, "with a moderately good grade of coal there should be no difficulty in furnishing the all the steam needed." No doubt.

The trio was later superheated; see Locobase 9398.

Class M-2 (Locobase 5344)

Described in the AERJ of February 1907, this engine was identical to the 3 M-1s delivered at the same time from the same builder except for the valves and cylinders and the provision of cylindrical Vanderbilt tenders. Although the same diameter and stroke, the Alfree-Hubbell offered a "delayed opening and closure for all points of cut-off, an increased exhaust area, and a large reduction in cylinder clearance." (The reader is then directed to AERJ September 1906). The effect is attained through an auxiliary, 5" piston valve with "wide special rings which fit openings in the wall between the steam port and exhaust passages"

AERJ noted that the system had been in service for over a year with "most satisfactory results both as regards economy of operation and maintenance, as well as in giving a very quick and responsive engine."

Locobase is not certain how widespread this installation might have been, but it must not have been very common nor is it likely to have remained on the M-2 for very long. The M-2 was later superheated -- see Locobase 9398 -- and carried on 'til 1956.

Class M-3 (Locobase 5346)

Described in the AERJ of February 1907, this was the odd-man-out among the 6 locomotives delivered at the same time. It was a Baldwin balanced compound with an extended wagon-top boiler. Steam was admitted through 15" piston valves. Its tender was a cylindrical Vanderbilt type.

Like Alco's M-4 Cole balanced compound, the M-3 soon was converted to a 2-cylinder simple-expansion locomotive. Still later it was superheated; see Locobase 9399.

Class M-4 (Locobase 5345)

Described in the AERJ of February 1907, this engine was identical to the 3 M-1s delivered at the same time in boiler and most other dimensions. Instead of the simple-expansion layout of the M-1, however, the M-4 was a Cole balanced compound similar (virtually identical, in fact) to the Q-2s delivered to the Northern Pacific in the same year. Like the NP engines, this engine had inside admission for the high-pressure piston valves, outside for the low-pressure ones. (The M-4 had a cylindrical Vanderbilt tender.)

Later converted to a 2-cylinder simple design, this engine carried on until 1957.

Class MR-1/MR-2/MR-4 (Locobase 9398)

Data from NdeM 1946 diagram book supplied in May 2005 by Allen Stanley from his extensive collection.

Locobases 5343, 5344, and 5345 show the M-1, M-2, and M-4 in their various saturated-boiler states. Sometime later the NdeM superheated all three classes to the same specification and redesignated them MR-1/MR-2 (R=recalentador or superheater). The 1946 book does not give an area for the superheater, so Locobase has made an estimate based on a very similar upgrade to the C & North Western E class. MR-2's big difference was an adhesion weight of 150,795 lb, while the MR-4 bulked up to 161,000 lb and had a firebox heating surface of 200 sq ft vs the 169 sq ft shown in the specs.

In any case, these engines soldiered on until the mid-1950s.

Class MR-3 (Locobase 9399)

Data from NdeM 1946 diagram book supplied in May 2005 by Allen Stanley from his extensive collection.

As delivered by Baldwin (Locobase 5346), this locomotive was a Baldwin balanced compound. Later the locomotive was simpled and still later superheated (hence the R in MR-3, which stands for "recalentador"). The superheater area is a Locobase estimate as the 1946 diagram does not provide a separate figure.

Class MR-6 (Locobase 1380)

Drury (1993) notes that the KR-1 Mikados, these MR-6s, and the PR-7 4-8-0s all had the same boiler (tubes, grate area, firebox identical). Of the first 20 delivered by Baldwin, 10 had Baker valve gear, 10 had Young gear; all had Ragonnet power reverse. The last was retired in 1962.

Railway Age (12 Nov 1921)

Class MR-7 (Locobase 9489)

Data from MexRy 1939 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

Delivered in the same year as the Mexican Railway's 3-cylinder engines (see Locobase 6744), these were carbon copies. The only differences were drivers measuring 2" smaller in diameter and larger tenders. Although they were Pacifics, the locomotives apparently served the NdeM in many capacities. They were rated to pull 2,300 tons in 57 cars on the level at 25 km/h (15 1/5 mph); at the other end of the spectrum, they were credited with the same speed hauling 4 cars in a train of 160 tons up a 4% grade.

Specifications
ClassM-1M-2M-3M-4MR-1/MR-2/MR-4MR-3MR-6MR-7
Locobase ID53435344534653459398939913809489
RailroadNacional de MexicoNacional de MexicoNacional de MexicoNacional de MexicoNacional de MexicoNacional de MexicoNacional de MexicoNacional de Mexico
Whyte4-6-24-6-24-6-24-6-24-6-24-6-24-6-24-6-2
Road Numbers2502-25042505250625072502-250525062511-2534178-179
GaugeStdStdStdStdStdStdStdStd
BuilderAlco-SchenectadyAlco-SchenectadyBurnham, Williams & CoAlco-SchenectadyNdeMNdeMBaldwinAlco-Schenectady
Year190619061906190619211928
Valve GearStephensonStephensonBakerBakerBaker
Locomotive Length and Weight
Driver Wheelbase12.25'12.25'12'12'12.25'12'12'13.83'
Engine Wheelbase33'33'33.92'34'33.75'34.75'33.17'34.50'
Ratio of driving wheelbase to overall engine wheebase 0.37 0.37 0.35 0.35 0.36 0.35 0.36 0.40
Overall Wheelbase (engine & tender)63.27'63.27'62.92'64.27'63.27'63.75'66.37'66.33'
Axle Loading (Maximum Weight per Axle)
Weight on Drivers141300 lbs141300 lbs147040 lbs150000 lbs144180 lbs150575 lbs159280 lbs154000 lbs
Engine Weight222500 lbs222500 lbs227340 lbs241000 lbs243386 lbs234900 lbs250870 lbs262000 lbs
Tender Light Weight135800 lbs135800 lbs142660 lbs136200 lbs147708 lbs146827 lbs169000 lbs
Total Engine and Tender Weight358300 lbs358300 lbs370000 lbs377200 lbs391094 lbs381727 lbs0431000 lbs
Tender Water Capacity7500 gals7500 gals7500 gals7500 gals7500 gals7500 gals8500 gals8500 gals
Tender Fuel Capacity (oil/coal)12 tons12 tons12 tons12 tons3120 gals2908 gals3500 gals3500 gals
Minimum weight per yard of rail on which locomotive could run78.50 lb rail78.50 lb rail81.69 lb rail83.33 lb rail80.10 lb rail83.65 lb rail88.49 lb rail85.56 lb rail
Geometry Relating to Tractive Effort
Driver Diameter67"67"67"67"67"67"67"67"
Boiler Pressure200 psi200 psi220 psi220 psi200 psi200 psi180 psi200 psi
Cylinders (dia x stroke)22" x 28"22" x 28"17" x 28"16.5" x 27"22" x 28"22" x 28"25" x 28"20" x 28" (3)
Tractive Effort34386 lbs34386 lbs33004 lbs29555 lbs34386 lbs34386 lbs39963 lbs42627 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.11 4.11 4.46 5.08 4.19 4.38 3.99 3.61
Heating Ability
Firebox Area210.30 sq. ft210.30 sq. ft186 sq. ft210.30 sq. ft169 sq. ft203 sq. ft228 sq. ft259 sq. ft
Grate Area51.60 sq. ft51.60 sq. ft52.10 sq. ft51.60 sq. ft51.43 sq. ft52.10 sq. ft66.60 sq. ft52 sq. ft
Evaporative Heating Surface37983798371337982983312035172823
Superheating Surface591591828760
Combined Heating Surface37983798371337983574371143453583
Evaporative Heating Surface/Cylinder Volume308.30308.30504.77568.39242.14253.26221.08184.85
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation1032010320114621135210286104201198810400
Same as above plus superheater percentage1032010320114621135211986.9012079.4514272.4812605.97
Same as above but substitute firebox area for grate area4206042060409204626639389.2047065.8048860.7462787.44
Power L18791.668791.665716.036924.0816582.6017139.1615299.9516025.05
Power MT411.51411.51257.11305.30760.68752.82635.31688.23

Credits

Introduction and specifications provided by Steve Llanso of Sweat House Media.

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